For sake of description simplicity, it is herein referred to coffee only, but more in general the present invention refers to any beverage obtained by infusion of a substance in form of powder or particles, such as tea, tisanes and similar, with water or other infusion liquid.
Machines for dispensing beverages are known, in particular for coffee and beverages of the same kind, having a dispensing apparatus for preparing coffee, where ground coffee is measured and inserted, by gravity, into an infusion chamber and then compressed by one or more movable walls, usually one or more pistons. An infusion liquid, usually water, is then forced through the coffee tablet compressed into the infusion chamber, so that the substances of the ground product are extracted and the beverage is obtained.
The amount of coffee powder to be settled inside the infusion chamber depends on the type of desired beverage: for example, for an espresso is necessary an amount of ground coffee much lower than the coffee amount necessary for a so-called “American” coffee. The ground coffee is fed by gravity into the infusion chamber and tends to settle inside the chamber randomly: in case of small coffee amount, little chambers have to be adopted in order to obtain beverages having acceptable qualities. Thereby there are dispensing machines having two infusion chambers, to be used based on the coffee amount to be dispensed into the infusion chamber: one with greater dimensions for greater amounts of coffee and one with smaller dimensions for beverages needing less coffee powder in the chamber, such as for example the “ristretto” and “espresso” coffee.
However such a solution is expensive to manufacture and needs an additional space in the dispensing machine. Furthermore, the presence of two infusion chambers increases the maintenance machine costs considerably.
Additional known problems of the dispensing assemblies refer to the repeatability of the beverage quality for all extractions.
In particular, during the “moistening” (or pre-infusion”) step, preferential paths originate inside the coffee tablet, along which the infusion liquid can pass through the tablet more easily, with a consequent non-optimal moistening of the coffee and a compromised extraction of substances from the ground coffee.
Furthermore it has to be considered that some machines provide for changes of their operative parameters based on the pressure detected on the piston that presses the coffee powder. Then a non-homogeneous distribution of the coffee powder inside the infusion chamber or frictions coming from movements can provide an inaccurate reading of pressure exercised during the coffee pressing.
Additional drawbacks caused by a non-homogeneous distribution of coffee powder can further be a greater wear of piston which compresses the coffee powder, with a consequent friction increase that could lead not only to a wrong reading of the forming pressure of the tablet, but also to damages of the piston itself.